Direct Peptide Reactivity Assay (DPRA)

The assessment of skin sensitization potential is an important component in the safety evaluation of substances and represents a standard requirement of legislation on chemicals. An in chemico assay, the Direct Peptide Reactivity Assay (DPRA), exploits the fact that most chemical allergens have electrophilic properties and are therefore able to react with the nucleophilic side chains of amino acids to form covalent bonds. The basic understanding of the assay is that if a chemical is capable of reacting with epidermal proteins then it has the potential to act as a sensitizer. The reactivity property can be described by the percentage of depletion of synthetic heptapeptides containing either cysteine or lysine over time following an approximate 24-hours incubation with the test article. The percentage of peptide depletion is measured by HPLC-UV detection. Percent peptide depletion is calculated from the following formula:

Reactivity data for chemical and ingredient libraries with applications in:

• Cosmetics and personal care product ingredients
• Agrichemical
• Biocides
• Specialty chemicals
• Pharmaceuticals

Direct Peptide Reactivity Assay Workflow

Mean of cysteine and lysine depletion	Reactivity class	Prediction
0% < Mean % depletion < 6.38%	Minimal reactivity	Non-sensitizer
6.38% < Mean % depletion < 22.62%	Low reactivity	Sensitizer
22.62% < Mean % depletion < 42.47%	Moderate reactivity	Sensitizer
42.47% < Mean % depletion < 100%	High reactivity	Sensitizer

Table1. Recommended classification of reactivity class and sensitization potential based on the DPRA data (cysteine 1:10/lysine 1:50 model).

Service features

• Quick results
• ECVAM validated protocol
• Cost efficient method for pre-screening and modifying new formulations

The Direct Peptide Reactivity Assay was recently validated by the European Center for the Validation of Alternative Methods and was endorsed by their scientific advisory group as a useful tool for early decision making during product screening and as a component in a weight-of-evidence approach or integrated testing strategy for safety/hazard assessment.

References:

1. Chin Lin Wong, et al. In vitro methods for hazard assessment of industrial chemicals – opportunities and challenges. Front. Pharmacol., 05 May 2015, doi10.3389
2. Gerberick, et al. Direct Peptide Reactivity Assay (DPRA) Method. Tox. Sci. 81, 332-343, 2004